TPT May 2008

T ube & P ipe W elding: T rends & P rogress

Achieving successful welding of titanium and its alloys

It will come as no surprise to fabricators with experience in handling titanium that special consideration needs to be taken during preparation and welding. Titanium and its alloys are reactive and can become contaminated by atmosphere gases. Adequate shielding using inert gas is

essential if repeatable, high quality joints are to be made. For many years it was believed that welding titanium could only be performed satisfactorily in sealed chambers equipped with glove ports and viewing ports, and filled with high purity inert gas such as argon. A better understanding of the mechanism of metal/gas interaction has shown that for some applications, as long as adequate local shielding is provided and maintained during welding, the use of sealed chambers with or without vacuum pumping systems may not be absolutely necessary. This understanding has afforded possibilities for welding large titanium fabrications and significantly extended the application areas for the metal and its alloys into major structural forms, especially

 Weld purge monitor

 Typical flexible titanium welding enclosure

in the aerospace industry, the motor sport industry and latterly in the petrochemical industry. The primary requirement then is to provide a protective gas atmosphere to the joint area during welding and subsequent cooling. The weld purge gas must be used correctly. It should be 99.999 per cent pure – even 99.995 per cent gas can lead to some yellow-straw discoloration. If the colour of the welded metal begins to mottle, or if it exhibits any hint of blue, then the gas is not pure enough, or has not been applied correctly. The gas flow should be started several seconds before welding. If there is enough

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M ay 2008

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